To the extent that supplemental oxygen after surgery is likely to reduce the incidence of major complications related to wound infection and healing, benefit is especially likely in morbidly obese patients because their baseline tissue oxygenation is usually sub-optimal and their risk is high. We thus propose to test the hypothesis that the incidence of major complications related to infection or inadequate healing are reduced in morbidly obese patients given 80% inspired oxygen during and for 12-18 hours after surgery compared with patients given 80% oxygen only during surgery.